Unite regional officer Lyn Turner said: "The management culture within Edinburgh Trams shows a pattern where the assumption of blame is the first choice of some managers.

"The management at Edinburgh Trams must know that workers cannot be motivated through blame or fear.

"Unite accepts that safety is the primary concern at all times. However the decision by management to escalate what we see as a few incidents that did not compromise safety to disciplinaries and sacking offences is simply unreasonable and unjust.

"These matters could have been dealt with quickly and fairly. Instead management have raised the bar and meted out punishment well beyond what was necessary, which has led to the decision to ballot our members for industrial action.

"We now have a situation where, because of the lack of rational decision-making by management, the trams may stop running."

An Edinburgh Trams spokeswoman said: "We take the responsibility of the safety of our customers and staff seriously, and we are confident in our internal processes.

"We are disappointed that Unite are not willing to allow the necessary time for these processes to formally conclude. We are not prepared to comment publicly on confidential staff matters.

"This is not a legal ballot, and we are surprised that Unite have chosen to take this action.